1. Field of the Invention
The field of art to which the invention pertains includes the field of defect planar mapping techniques, particularly with respect to a method of planar mapping a transparent surface and producing a permanent record of defects therein.
2. Description of the Prior Art
Prior techniques for inspecting transparent material for flaws included directing a light source at an angle to the material surface. The light source was then swept across the entire surface and defects visually noted by the inspector. The angle of available lighting, illumination brightness, light scattering, and visual acuity of the observer combined to make the flaw detection technique extremely difficult especially where the transparent material had already been installed. Alternative techniques included the use of light measuring devices wherein a source of light was passed through the window and a light detector measured the amount of transmitted light. These systems are extremely complex and the sensitivity thereof is dependent upon the components available for transmitting and measuring the light. In addition, minute flaws on the transparent surface are normally undetectable by such techniques.
For example, in spacecraft windows, which are normally made of one-inch thick transparent material, the maximum acceptable flaw on the surface is a six ten-thousandth inch (0.0157 mm) surface defect. Should the surface defect be greater than six ten-thousandths of an inch (0.0152 mm) deep, for one-inch material, the spacecraft window is deemed unsafe for space flight where the window will be subjected to large variations in pressure between the surfaces of the window, as well as other wide variations in temperature and environmental conditions.
Known prior art includes U.S. Pat. Nos. 3,652,863; 3,639,067; 1,514,368; and 552,641.
The present invention provides a method of detecting flaws on the surface as well as the interior of a transparent material and providing a permanent record thereof. The record can then be reviewed to determine the flaws existing in the transparent material as well as their position. Once the position of the flaws have been noted, further inspection can be utilized to determine the extent or depth of the flaws.